We will prepare total polysomal mRNP from chick embryo cerebra by equilibrium sedimentation in dense, non-ionic media. This technique, which we have developed, allows the preparation of unaltered mRNP relatively free of ribosomal subunits. We will study the stoichiometry of binding of mRNP proteins to mRNA, and we will use an homologous cell-free translation system to evaluate their function.